On a sidenote: Roxio's Toast also has the ability to compare disks and folders (this functionality has been there for ages), and it provides a color-coded output, where you can easily see which files have been changed, removed, or added. I hope Apple will add something similar to FileMerge in the future.
[robg adds: I had no idea this functionality was buried in FileMerge. Quite useful if you do a lot of transferring of folders between machines...]

